Escherichia coli (E. coli) bacteria are ordinarily harmless bacteria found as part of the natural microbial flora in a number of animals. In humans, E. coli form a major part of the natural flora of the large intestine. Some types of E. coli, however, have the capacity to invade the tissue of their host, resulting in severe, and ofttimes fatal, disease.
In poultry, invasive E. coli cause colisepticemia: the disease that results in the greatest loss to poultry producers in the United States and worldwide of all poultry diseases. In calves and pigs, neonatal colisepticemia is a major cause of mortality, and in humans--particularly among infants in third-world countries--E. coli can invade the blood and the membranes which envelope the brain and spinal cord to produce neonatal meningitis.
There has not heretofore been available a simple, reliable test for distinguishing invasive, disease-causing E. coli from harmless, noninvasive E. coli in an undifferentiated bacterial sample taken form a host organism (a sample which contains a number of distinct types of bacteria). Such a test would, however, have a profound impact on the prevention and control of septicemic E. coli infections in animals and humans.
Previously, such diseases were diagnosed by isolating E. coli from tissue which would normally be free of bacteria (such as the liver and brain) after the tissue had been invaded, or by the use of serotyping. Serotyping, a widely used procedure by which bacteria are classified according to the kinds and combinations of antigens found on each strain of bacteria, has proven to be unreliable for this particular purpose.
Payne and Finkelstein, Infection and Immunity, 18, 94 (1977) found that colonies of a previously isolated and established strain of virulent E. coli bacteria were stained when raised on a growth media containing Congo Red dye, while nonvirulent variants of that strain were not stained by the dye. They suggest that their procedure could be useful for selecting the few harmless mutants which can be found in a previously isolated strain of virulent bacteria so that the harmless mutants could be used in vaccines. No suggestion is made that the procedure would be useful for detecting the few invasive E. coli in an undifferentiated bacterial sample taken from a host organism--a sample which would be largely comprised of harmless strains of E. coli.
The manner by which colisepticemia is transmitted in poultry has not been well understood. It has generally been believed to arise as a secondary infection following a primary infection by a virus, mycoplasma, or other virulent microbe. Barbour, Nabbut and Al-Nakhli, Am. J. Vet. Res., 46, 989 (1985), who investigated the source of E. coli infections in poultry by collecting bacterial samples from hearts and livers of dead and moribund birds, generally suggest the breeding farm as the main source of the problem, but they used serotyping to distinguish invasive from noninvasive E. coli--a procedure which does not produce reliable results for this purpose. No suggestion is made as to how colisepticemia could be predicted in a poultry flock without the use of serotyping, and without the use of bacteria obtained from tissue samples.